Rosin-derived cationic compounds and polymers

ABSTRACT

Methods for forming rosin-derived cationic compounds are provided. The method can include attaching a cationic group to a conjugated diene on a hydrophenathrene-based ring of a resin acid (e.g., levopimaric acid, abietic acid, dehydroabietic acid, or a mixture thereof) to form a rosin-derived cationic compound. Attaching the cationic group to the conjugated diene on the hydrophenathrene-based ring of the resin acid can be achieved via a Diels-Alder reaction of a dienophile with the hydrophenathrene-based ring of the resin acid. Rosin-derived cationic compounds are also provided. The rosin-derived cationic compound can include a cationic group attached to a conjugated diene on a hydrophenathrene-based ring of a resin acid, wherein the rosin-derived cationic compound further comprises a carboxylic acid group.

PRIORITY INFORMATION

The present application claims priority to, and is a divisionalapplication of, U.S. patent application Ser. No. 13/396,877 titled“Rosin-Derived Cationic Compounds and Polymers Along with Their Methodsof Preparation” filed on Feb. 15, 2012 of Tang, et al. and to U.S.Provisional Patent Application Ser. No. 61/463,304 titled “Rosin-DerivedCationic Compounds and Polymers and Their Methods of Preparation” filedon Feb. 15, 2011 by Tang, et al.; both of which are incorporated byreference herein.

BACKGROUND

Synthetic plastics account for the use of 7% of fossil fuels in theworld. The limited resources and rising price of fossil fuels present achallenge to seek developing renewable resources for manufacturing of“green” plastics. However, applications of renewable polymers lagsignificantly behind petrochemical-derived polymers, partially becauseof limitations in the monomer resources and the derived polymers withcontrolled properties.

As such, synthesis of renewable compounds and polymer-based materialsfrom natural resources has attracted significant attentions, as thesecompounds and materials have the promise to replace compounds andplastics derived from petroleum chemicals. Cationic compounds have manyapplications such as antimicrobials, biocides, antibiotics, drug,surfactants, etc. Cationic polymers have many applications such asantimicrobial materials, antifouling coatings, packaging materials,surfactants, for use in water sanitation and purification, and in drugdelivery, etc.

Produced in quantities of more than one million tons annually, rosin(including gum rosin, wood rosin and tall rosin), whose major componentsare resin acids (or rosin acids) including abietic acid, levopimaricacid, hydroabietic acid, dehydroabietic acid, pimaric acid, is generallyused as ingredients for inks, vanishes, adhesives, cosmetics, medicines,chewing gums, etc. Rosin acids have three characteristicfunctionalities: hydrophenanthrene rings, carboxylic acid, andconjugated dienes.

Rosin has been used as raw materials to prepare cationic compounds. Forexample, rosin has been widely used as raw materials to preparepolymeric materials, in which rosin moieties are placed either at thebackbone or at the side groups. Radical polymerization has been used toprepare vinyl polymers, while condensation polymerization has producedmany polymers. (See e.g., U.S. Patent Publication No. 2011/0086979 ofChuanbing Tang titled “Polymers Derived from Rosin and Their Methods ofPreparation”).

However, the cationic group is, in these methods, attached to the rosinmoiety through the carboxylic acid group. Thus, the most readilyfunctionalizable group of the rosin moiety (i.e., the carboxylic acidgroup) is no longer available for further reaction according to thesemethods. Such limited functionality hinders the usefulness of thepolymers formed according to these methods.

As such, a need exists for methods of preparing cationic compounds andcationic polymers from rosin (e.g., resin acids) without utilizing thecarboxylic acid group of the rosin moiety.

SUMMARY

Objects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

Methods are generally provided for forming rosin-derived cationiccompounds. In one embodiment, the method can include attaching acationic group to a conjugated diene on a hydrophenathrene-based ring ofa resin acid (e.g., levopimaric acid, abietic acid, dehydroabietic acid,or a mixture thereof) to form a rosin-derived cationic compound. Forexample, attaching the cationic group to the conjugated diene on thehydrophenathrene-based ring of the resin acid can comprise reacting adienophile with the hydrophenathrene-based ring of the resin acid via aDiels-Alder reaction.

In one particular embodiment, the rosin-derived cationic compound caninclude a carboxylic acid group. As such, the method can further includereacting the carboxylic acid group on the rosin-derived cationiccompound with a polymerizable group to form a functionalizedrosin-derived cationic compound having a polymerizable functional group.The method can, in one embodiment, then further include polymerizing aplurality of the functionalized rosin-derived cationic compounds havinga polymerizable functional group (e.g., a vinyl group) via controlledpolymerization into a polymeric material, wherein each polymer defines afunctional end group (e.g., a vinyl group), and wherein the polymericmaterial has a polydispersity index of about 1 to about 1.5 (e.g., about1.05 to about 1.45).

For example, the method can further include reacting the carboxylic acidgroup on the rosin-derived cationic compound with an amine to form thefunctionalized rosin-derived cationic compound having the vinylfunctional group. Alternatively, the method can further include reactingthe carboxylic acid group on the rosin-derived cationic compound with analcohol (e.g., hydroxyalkyl (meth)acrylate, such as hydroxyalkylmethacrylate) to form the functionalized resin acid having a vinylfunctional group.

The plurality of rosin-derived cationic compounds can be, in particularembodiments, polymerized via controlled living polymerization. Forexample, controlled living polymerization can be atom transfer radicalpolymerization, wherein the rosin-derived cationic compounds arepolymerized in a polymerization solution comprising the rosin-derivedcationic compound, an initiator (e.g., an organic halide such as analkyl halide), a ligand, and a catalyst (e.g., copper(I)).Alternatively, controlled living polymerization can be reversibleaddition-fragmentation chain transfer polymerization, wherein therosin-derived cationic compounds are polymerized in a polymerizationsolution comprising the rosin-derived cationic compound, an initiator(e.g., azobisisobutyronitrile, 4,4′-azobis(4-cyanovaleric acid), orcombinations thereof), and a chain transfer agent (e.g., athiocarbonylthio compound).

Rosin-derived cationic compounds are also generally provided, such asthose formed according to any of the presently disclosed methods. In oneembodiment, the rosin-derived cationic compound can include a cationicgroup attached to a conjugated diene on a hydrophenathrene-based ring ofa resin acid, wherein the rosin-derived cationic compound furthercomprises a carboxylic acid group.

Other features and aspects of the present invention are discussed ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof to one skilled in the art, is set forth moreparticularly in the remainder of the specification, which includesreference to the accompanying figures, in which:

FIG. 1 shows an exemplary reaction method for synthesis of quaternaryammonium-containing rosin acid 1 and rosin ester 2;

FIG. 2 shows an exemplary reaction method for synthesis of quaternaryammonium-containing rosin-derived methacrylate polymer 4;

FIG. 3 shows an exemplary reaction method synthesis of degradablequaternary ammonium-containing rosin-derived polycaprolactone 6;

FIG. 4 shows an exemplary reaction method synthesis of quaternaryammonium-containing rosin-derived block copolymer 7;

FIG. 5 shows an exemplary reaction method synthesis of phosphoniumsalts-containing rosin acid 8 and rosin ester 9;

FIG. 6 shows an exemplary reaction method synthesis of sulfoniumsalts-containing rosin acid 10 and rosin ester 11; and

FIG. 7 shows an Agar diffusion method to test antibacterial activity ofrosin-derived quaternary ammonium and its polymer (at differentconcentrations) against Staphylococcus aureus.

FIG. 8 shows an exemplary scheme for the synthesis of quaternaryammonium-containing resin acid-derived antimicrobial compounds andpolymers.

DEFINITIONS

As used herein, the term “polymer” generally includes, but is notlimited to, homopolymers; copolymers, such as, for example, block,graft, random and alternating copolymers; and terpolymers; and blendsand modifications thereof. Furthermore, unless otherwise specificallylimited, the term “polymer” shall include all possible geometricalconfigurations of the material. These configurations include, but arenot limited to isotactic, syndiotactic, and atatic symmetries.

The term “organic” is used herein to pertaining to a class of chemicalcompounds that are comprised of carbon atoms. For example, an “organicpolymer” is a polymer that includes carbon atoms in the polymerbackbone.

The “number average molecular weight” (M_(n)) is readily calculated byone of ordinary skill in the art, and generally refers to the ordinaryarithmetic mean or average of the molecular weights of the individualmacromolecules. It is determined by measuring the molecular weight of npolymer molecules, summing the weights, and dividing by n, such asrepresented in the formula:

${\overset{\_}{M}}_{n} = \frac{\sum\limits_{i}{N_{i}M_{i}}}{\sum\limits_{i}N_{i}}$where N₁ is the number of molecules of molecular weight M_(i). Thenumber average molecular weight of a polymer can be determined by gelpermeation chromatography and all colligative methods, like vaporpressure osmometry or end-group determination.

The “weight average molecular weight” (M_(w)) is readily calculated byone of ordinary skill in the art, and generally refers to:

${\overset{\_}{M}}_{w} = \frac{\sum\limits_{i}{N_{i}M_{i}^{2}}}{\sum\limits_{i}{N_{i}M_{i}}}$where N_(i) is the number of molecules of molecular weight M_(i). Theweight average molecular weight can be determined by gel permeationchromatography, light scattering, small angle neutron scattering (SANS)and X-ray scattering.

The polydispersity index (PDI) is a measure of the distribution ofmolecular mass in a given polymer sample. The PDI calculated is theweight average molecular weight divided by the number average molecularweight (i.e., PDI=M_(w)/M_(n)). It indicates the distribution ofindividual molecular masses in a batch of polymers. The PDI has a valueequal to or greater than 1, but as the polymer chains approach uniformchain length, the PDI approaches unity (i.e., 1).

DETAILED DESCRIPTION

Reference now will be made to the embodiments of the invention, one ormore examples of which are set forth below. Each example is provided byway of an explanation of the invention, not as a limitation of theinvention. In fact, it will be apparent to those skilled in the art thatvarious modifications and variations can be made in the inventionwithout departing from the scope or spirit of the invention. Forinstance, features illustrated or described as one embodiment can beused on another embodiment to yield still a further embodiment. Thus, itis intended that the present invention covers such modifications andvariations as come within the scope of the appended claims and theirequivalents. It is to be understood by one of ordinary skill in the artthat the present discussion is a description of exemplary embodimentsonly, and is not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied exemplary constructions.

Generally speaking, the preparation of rosin-derived cationic compoundsand cationic polymers is disclosed through functionalization ofconjugated dienes of rosin moieties. Compositions are also generallydisclosed of rosin-containing cationic compounds and polymers, alongwith methods of their formation and use.

Through these methods, rosin components (e.g., resin acids) can beintegrated as part of renewable monomer units, and the cationic groupcan be part of rosin moiety. The cationic group can be quaternaryammonium, phosphonium, sulfonium, or a mixture thereof. Therosin-containing cationic compounds can have various applications suchas antimicrobial reagents, biocides, antibiotics, drug, surfactants,etc.

Homopolymers can also be formed according to certain embodiments thatcan contain rosin-derived cationic units, where the units can be: (a)non-degradable monomers such as acrylates, methacrylates, acrylamides,styrenes; (b) degradable monomers such as caprolactone, lactide,glycolic acid, hydroxyalkanoic acids, hydroxybutyric acid,hydroxyvaleric acid, and trimethylene carbonate; or the like.

Rosin-containing cationic polymers for organic/inorganic nanocompositescan also be formed according to certain embodiments. Suchrosin-containing cationic polymers can be star copolymers, graftedcopolymers, etc. Rosin-containing cationic polymers can have variousapplications such as antimicrobial materials, antifouling coatings,packaging materials, surfactants, for use in water sanitation andpurification, and in drug delivery, etc.

The properties of rosin-containing cationic polymers can be tuned bychanging the molecular weight, compositions and chemical structures ofeach segment.

Rosin is a renewable biomass that includes resin acids (or rosin acids),such as levopimaric acid, abietic acid, hydroabietic acid,dehydroabietic acid, maleopimaric acid, etc. Such resin acids are usedas substrates to prepare cationic compounds and/or cationic polymers.Thus, an entirely new approach is generally provided to developrosin-containing cationic compounds and cationic polymers inapplications such as drugs, antibiotics, antimicrobial materials,antifouling coatings, packaging materials, surfactants, for use in watersanitation and purification, and in drug delivery, etc. Successfulimplementation of these cationic compounds and cationic polymers canalso provide a replacement of some of petrochemical-based chemicals andpolymers, thus reducing consumption of major synthetic polymers derivedfrom fossil fuels.

In particular embodiments, methods are provided for preparingrosin-containing cationic compounds and cationic polymers, where: thecationic compounds contain at least part of molecules derived fromrosin; the cationic homopolymers contain rosin-derived side groups; thecationic block copolymers, graft copolymers, star copolymers and/ororganic/inorganic hybrids contain at least one segment derived fromrosin; the cationic block copolymers, graft copolymers, star copolymersand/or organic/inorganic hybrids contain at least one polymerizedmonomer derived from rosin and rosin-derived side groups; the cationichomopolymers, block copolymers, graft copolymers, star copolymers and/ororganic/inorganic hybrids have controllable compositions, and molecularweight; and combinations thereof.

I. Rosin-Derived Resin Acids

Rosin's major components include resin acids, which can be obtained frompine trees and other plants, in a number of isomeric forms. Generally,the resin acids have a three ring structure (e.g., ahydrophenanthrene-based three ring structure) with a carboxylic acidfunctional group (i.e., —COOH). Prevalent resin acids include, but arenot limited to, abietic acid, neoabietic acid, dehydroabietic acid,palustric acid, levopimaric acid, pimaric acid, isopimaric acids, etc.Nearly all resin acids have the same basic skeleton of a 3-ring fusedsystem with the empirical formula C₁₉H₂₉COOH.

Six particularly suitable resin acids for use as monomers in thepresently disclosed methods and polymers include levopimaric acid,abietic acid, dehydroabietic acid, hydroabietic acid, pimaric acid,isopimaric acid, and mixtures thereof due to their availabilitycommercially at various purities. Each of these resin acids have acarboxylic acid group (i.e., R—COOH) attached to thehydrophenathrene-based rings.

However, resin acids having conjugated dienes on itshydrophenathrene-based ring are particularly suitable for reaction witha cationic group while leaving the carboxylic acid group unchanged inthe resulting rosin-derived cationic compound. The chemical structuresof particularly suitable resin acids, which have conjugated dienes onits hydrophenathrene-based ring, are provided below and are generallyknown in the art:

As shown, each of these resin acids has conjugated dienes on itshydrophenathrene-based ring.

The resin acid or mixture of resin acids (collectively referred to as“resin acid(s)”) can be purified through standard techniques to providea substantially pure resin acid(s) starting material for the polymers.For example, the resin acid or mixture of resin acids can be purified toat least about 95% by weight, such as at least about 98% by weight.

In particular embodiments, the resin acid or mixture of resin acids canbe purified to be about 99% by weight to substantially free from othermaterials. As used herein, the term “substantially free” means no morethan an insignificant trace amount present and encompasses completelyfree (e.g., 0% by weight up to about 0.0001% by weight). Thus, most orsubstantially all of the other organic material in the rosin can beseparated from the resin acid(s) prior to functionalization.

In alternative embodiments, the resin acid(s) can be utilizedcollectively in their natural rosin form.

II. Functionalized Resin Acids

In one particular embodiment, a functionalized resin acid is providedthat still includes its carboxylic acid group. For example, a resin acidthat has at least two conjugated dienes on its hydrophenathrene-basedring can be reacted with a dienophile via a Diels-Alder reaction. In atypical Diels-Alder reaction, the dienophile has an electron-withdrawinggroup conjugated to an alkene, though this feature is not exclusive ofDiels-Alder dienophiles. In certain embodiments, the dienophile can beactivated by a Lewis acid such as niobium pentachloride. Additionally,the Diels-Alder reaction can be carried out in the presence of ethylacetate.

Suitable dienophiles for reaction with the conjugated dienes of theresin acid include, but are not limited to, maleic anhydride,cyclohexenone, styrene, acrylic acid, methacrylic acid, acrylamide,methacrylamide, or mixtures and/or derivatives thereof.

For example, FIGS. 1-4 show exemplary reactions involving maleicanhydride with the conjugated dienes of the resin acid. Alternatively,FIGS. 5 and 6 show exemplary reactions involving a styrene derivativewith the conjugated dienes of the resin acid.

III. Rosin-Derived Cationic Compounds

Rosin-derived cationic compounds and their synthesis are generallydescribed in one particular embodiment. Specifically, methods aredisclosed of preparing cationic compounds and cationic polymers fromrosin (e.g., resin acids) without utilizing the carboxylic acid group ofthe rosin moiety, along with the resulting compounds. For instance, thecationic group (e.g., a quaternary ammonium group) can be attachedthrough functionalization of conjugated dienes of rosin moieties.

In particular, the resin acid(s) can be functionalized withpolymerizable groups, such as vinyl groups (e.g., an acrylate group, amethacrylate group, etc.) or strained ring functional groups (e.g.,cyclic ester groups like caprolactone or lactide, a norbornene group, acyclopentene group, etc.). Specifically, the conjugated dienes on itshydrophenathrene-based ring can be functionalized into the polymerizablegroups.

For example, FIG. 1 shows a quaternary ammonium-containing rosin acid 1prepared through a Diels-Alder reaction between levopimaric acid andmaleic anhydride followed by an amidation and a quaternization reaction.The quaternary ammonium-containing rosin acid 1 can be further convertedto the quaternary ammonium-containing rosin ester 2 through anesterification reaction. Although shown as a cationic quaternaryammonium unit in the reaction of FIG. 1, this unit can be substituted orreplaced with other cationic units, e.g. phosphonium, sulfonium.

In one embodiment, the rosin unit can be derived through thermalisomerization of other acid forms, e.g. abietic acid. Likewise, theester group can be replaced by other groups such as alcohols, amides,ethers, alkyl halides, epoxides, aldehydes, alkenes, alkynes, etc.

Thus, FIG. 1 illustrates a scheme for one particular embodiment—the caseof quaternary ammonium-containing rosin acid (1) and rosin ester (2), asdescribed further in the Examples.

IV. Rosin-Derived Monomers

Rosin-derived monomers can also be formed utilizing the rosin-derivedcationic compounds. For example, the carboxylic acid group on therosin-derived cationic compound can be functionalized into monomerscontaining the Diels-Alder adduct (e.g., an anhydride adduct) and apolymerizable functional group. For instance, the polymerizablefunctional group can be attached to the rosin-derived cationic compoundvia its carboxylic acid group. Particularly suitable methods forattaching a polymerizable functional group to the carboxylic acid groupof a resin acid are described in U.S. Patent Publication No.2011/0086979 of Chuanbing Tang titled “Polymers Derived from Rosin andTheir Methods of Preparation,” which is incorporated by referenceherein.

V. Polymerization of Rosin-Derived Monomers

Polymers that can be formed according to the presently disclosedmethods, include, but are not limited to, homopolymers, blockcopolymers, graft polymers, star polymers, organic polymers/inorganichybrids, etc. In one particular embodiment, these polymer compositionscan also have controlled molecular weight and/or can be formed fromrosin derivatives and degradable polymers. Degradable polymers compriseat least one of repeating units: caprolactone, lactide, lactic acid,glycolic acid, hydroxyalkanoic acids, hydroxybutyric acid,hydroxyvaleric acid, trimethylene carbonate, dicarboxylic acidanhydrides, butylene succinate, and butylene adipate.

Additionally, in certain embodiments, well-defined rosin-derivedpolymers and their methods of production are provided. Thus, asynergistic strategy has been developed to form well-defined polymersfrom a renewable resource—rosin, which is an exudate from pine trees andother plants. Accordingly, well-defined rosin-derived polymers withcontrolled molecular weight, low polydispersity, chemical topologies andend group functionality can be developed to provide tailored propertiesfor applications in the areas of thermoplastic resins, thermoplasticelastomers, adhesives, printing inks, paper-sizing, varnishes, coatings,nanocomposites, shape memory materials, anti-fouling materials,nanoporous membranes, etc.

The presently disclosed methods can allow for controllable molecularweight, low polydispersity and varied chemical topologies and chainfunctionality of the polymers. Thus, a broad strategy is generallydisclosed allowing for the development of well-defined polymers derivedfrom renewable resources, which can provide access to diverse polymersthat rosin offers, but with controlled structures and molecular weight.Successful implementation of these rosin-based polymers can lead toreplacement of petrochemical-based polymers, thus reducing consumptionof major synthetic polymers from fossil fuels.

More particularly, methods are provided for preparing well-definedpolymers from rosin based materials (e.g., rosin based monomers, such asmodified resin acids). The well-defined polymers can include blockcopolymers, random copolymers, graft copolymers, star copolymer, ororganic/inorganic hybrids that contain at least one polymerized monomerderived from rosin. Such well-defined polymers have controllablecompositions, controllable molecular weight, a narrow molecular weightdistribution, and end group functionality.

Rosin-derived polymers developed according to the present disclosure canhave applications ranging from thermoplastic resins, thermoplasticelastomers, varnishes, wax, paper sizing, adhesives, coatings, printinginks to shape memory polymers, nanocomposites, pharmaceutics,anti-fouling, nanoporous membrane, etc.

In certain embodiments, the functionalized resin acid(s) can besubjected to controlled polymerizations, such as controlled livingpolymerizations (CLPs) or controlled ring-opening polymerizations.Through the use of these controlled polymerizations, polymers can beproduced with low polydispersity, high functionality (e.g., a terminalfunctional group), and diverse architectures. Thus, these methods areideal for block polymer and/or graft polymer synthesis.

Controlled living polymerization generally refers to chain growthpolymerization which proceeds with significantly suppressed terminationor chain transfer steps. Thus, polymerization in CLP proceeds until allmonomer units have been consumed, and the addition of monomer results incontinued polymerization, making CLP ideal for block polymer and graftpolymer synthesis. The molecular weight of the resulting polymer isgenerally a linear function of conversion so that the polymeric chainsare initiated and grow substantially uniformly. Thus, CLPs provideprecise control on molecular structures, functionality and compositions.Thus, these polymers can be tuned with desirable compositions andarchitectures.

Controlled living polymerizations can be used to produce blockcopolymers because CLP can leave a functional terminal group on thepolymer formed (e.g., a halogen functional group). For example, in thecopolymerization of two monomers (A and B) allowing A to polymerize viaCLP will exhaust the monomer in solution with minimal termination. Aftermonomer A is fully reacted, the addition of monomer B will result in ablock copolymer.

Controlled ring-opening polymerizations can utilize suitable catalystssuch as tin(II) to open the rings of monomers to form a polymer.

The functionalized resin acid(s) can be polymerized alone (e.g., as asingle resin acid or a combination of multiple resin acids) or withother monomers (e.g., styrene, methacrylate, acrylate, lactide,caprolactone, etc., or combinations thereof). As such, in specificembodiments, block copolymers, random copolymers, graft copolymers, starcopolymer or organic/inorganic hybrids can each bear other monomer unitsselected from olefins, conjugated dienes, methacrylates, styrenes,acrylates, acrylamides, and acrylonitriles, esters, ethers, urethanes,ureas, amides and other functional monomer units thereof.

Specific polymerization techniques can be utilized to form thewell-defined polymers, as discussed in greater detail below.

A. Atom Transfer Radical Polymerization

Atom transfer radical polymerization (ATRP) is an example of a livingradical polymerization. The control is achieved through anactivation-deactivation process, in which most of the reaction speciesare in dormant format, thus significantly reducing chain terminationreaction. The four major components of ATRP include the monomer,initiator, ligand, and catalyst. ATRP is particularly useful where thefunctionalized resin acid(s) have a vinyl functional group (e.g., a(meth)acrylate group).

Organic halides are particularly suitable initiators, such as alkylhalides (e.g., alkyl bromides, alkyl chlorides, etc.). For instance, inone particular embodiment, the alkyl halide can be ethyl2-bromoisobutyrate. The shape or structure of the initiator can alsodetermine the architecture of the resulting polymer. For example,initiators with multiple alkyl halide groups on a single core can leadto a star-like polymer shape.

The catalyst can determine the equilibrium constant between the activeand dormant species during polymerization, leading to control of thepolymerization rate and the equilibrium constant. In one particularembodiment, the catalyst is a metal having two accessible oxidationstates that are separated by one electron, and a reasonable affinity forhalogens. One particularly suitable metal catalyst for ATRP is copper(I).

The ligands can be linear amines or pyridine-based amines.

Depending on the target molecular weight of final polymers, the monomerto initiator ratios can range from less than about 10 to more than about1,000 (e.g., about 10 to about 1,000). Other reaction parameters can bevaried to control the molecular weight of the final polymers, such assolvent selection, reaction temperature, and reaction time. Forinstance, solvents can include conventional organic solvents such astetrahydrofuran, toluene, dimethylformamide, anisole, acetonitrile,dichloromethane, etc. The reaction temperature can range from roomtemperature (e.g., about 20° C.) to about 120° C. The reaction time canbe from less than about 1 h to about 48 h.

B. Reversible Addition-Fragmentation Chain Transfer Polymerization

Reversible Addition-Fragmentation chain Transfer polymerization (RAFT)is another type of controlled radical polymerization. RAFTpolymerization uses thiocarbonylthio compounds, such as dithioesters,dithiocarbamates, trithiocarbonates, and xanthates, in order to mediatethe polymerization via a reversible chain-transfer process. RAFTpolymerization can be performed by simply adding a chosen quantity ofappropriate RAFT agents (thiocarbonylthio compounds) to a conventionalfree radical polymerization. RAFT polymerization is particularly usefulwhere the functionalized resin acid(s) have a vinyl functional group(e.g., a (meth)acrylate group).

Typically, a RAFT polymerization system includes the monomer, aninitiator, and a RAFT agent (also referred to as a chain transferagent). Because of the low concentration of the RAFT agent in thesystem, the concentration of the initiator is usually lower than inconventional radical polymerization. Suitable radical initiators can beazobisisobutyronitrile (AIBN), 4,4′-azobis(4-cyanovaleric acid) (ACVA),etc.

RAFT agents are generally thiocarbonylthio compounds, such as generallyshown below:

where the z group primarily stabilizes radical species added to the C═Sbond and the R group is a good homolytic leaving group which is able toinitiate monomers. For example, the z group can be an aryl group (e.g.,phenyl group, benzyl group, etc.), an alkyl group, etc. The R″ group canbe an organic chain terminating with a carboxylic acid group.

As stated, RAFT is a type of living polymerization involving aconventional radical polymerization in the presence of a reversiblechain transfer reagent. Like other living radical polymerizations, thereis minimized termination step in the RAFT process. The reaction isstarted by radical initiators (e.g., AIBN). In this initiation step, theinitiator reacts with a monomer unit to create a radical species whichstarts an active polymerizing chain. Then, the active chain reacts withthe thiocarbonylthio compound, which kicks out the homolytic leavinggroup (R″). This is a reversible step, with an intermediate speciescapable of losing either the leaving group (R″) or the active species.The leaving group radical then reacts with another monomer species,starting another active polymer chain. This active chain is then able togo through the addition-fragmentation or equilibration steps. Theequilibration keeps the majority of the active propagating species intothe dormant thiocarbonyl compound, limiting the possibility of chaintermination. Thus, active polymer chains are in an equilibrium betweenthe active and dormant species. While one polymer chain is in thedormant stage (bound to the thiocarbonyl compound), the other is activein polymerization.

By controlling the concentration of initiator and thiocarbonylthiocompound, the molecular weight of the polymers can be controlled withlow polydispersities.

Depending on the target molecular weight of final polymers, the monomerto RAFT agent ratios can range from about less than about 10 to morethan about 1000 (e.g., about 10 to about 1,000). Other reactionparameters can be varied to control the molecular weight of the finalpolymers, such as solvent selection, reaction temperature, and reactiontime. For instance, solvents can include conventional organic solventssuch as tetrahydrofuran, toluene, dimethylformamide, anisole,acetonitrile, dichloromethane, etc. The reaction temperature can rangefrom room temperature (e.g., about 20° C.) to about 120° C. The reactiontime can be from less than about 1 h to about 48 h.

The RAFT process allows the synthesis of polymers with specificmacromolecular architectures such as block, gradient, statistical,comb/brush, star, hyperbranched, and network copolymers.

Because RAFT polymerization is a form of living radical polymerization,it is ideal for synthesis of block copolymers. For example, in thecopolymerization of two monomers (A and B) allowing A to polymerize viaRAFT will exhaust the monomer in solution with significantly suppressedtermination. After monomer A is fully reacted, the addition of monomer Bwill result in a block copolymer. One requirement for maintaining anarrow polydispersity in this type of copolymer is to have a chaintransfer agent with a high transfer constant to the subsequent monomer(monomer B in the example).

Using a multifunctional RAFT agent can result in the formation of a starcopolymer. RAFT differs from other forms of CLPs because the core of thecopolymer can be introduced by functionalization of either the R groupor the Z group. While utilizing the R group results in similarstructures found using ATRP or NMP, the use of the Z group makes RAFTunique. When the Z group is used, the reactive polymeric arms aredetached from the core while they grow and react back into the core forthe chain-transfer reaction.

C. Nitroxide-Mediated Polymerization

Nitroxide-mediated polymerization (NMP) is another form of controlledliving polymerization utilizing a nitroxide radical, such as shownbelow:

where R1 and R2 are, independently, organic groups (e.g., aryl groupssuch as phenyl groups, benzyl groups, etc.; alkyl groups, etc.). NMP isparticularly useful where the functionalized resin acid(s) have a vinylfunctional group (e.g., a (meth)acrylate group).

D. Ring-Opening Metathesis Polymerization

Ring-opening metathesis polymerization (ROMP) is a type of olefinmetathesis polymerization. The driving force of the reaction is reliefof ring strain in cyclic olefins (e.g. norbornene or cyclopentene) inthe presence of a catalyst. The catalysts used in a ROMP reaction caninclude a wide variety of metals and range from a simple RuCl₃/alcoholmixture to Grubbs' catalyst.

In this embodiment, the functionalized resin acid can include a strainedring functional group, such as a norbornene functional group, acyclopentene functional group, etc. to form the rosin derived polymers.For example, norbornene is a bridged cyclic hydrocarbon that has acyclohexene ring bridged with a methylene group in the para position.

The ROMP catalytic cycle generally requires a strained cyclic structurebecause the driving force of the reaction is relief of ring strain.After formation of the metal-carbene species, the carbene attacks thedouble bond in the ring structure forming a highly strainedmetallocyclobutane intermediate. The ring then opens giving thebeginning of the polymer: a linear chain double bonded to the metal witha terminal double bond as well. The new carbene reacts with the doublebond on the next monomer, thus propagating the reaction.

E. Ring-Opening Polymerization

In one particular embodiment, where the functionalized resin acidincludes a strained ring function group (e.g., a caprolactone orlactide), ring-opening polymerization (ROP) may be used to form therosin derived polymers. For example, a rosin-substituted caprolactone isa polymerizable ester, which can undergo polymerization with the aid ofan alcohol as an initiator and a tin-based reagent as a catalyst.

VI. Rosin-Derived Polymers and Block Co-Polymers

Through CLP, the resulting polymeric material can include well-definedpolymers, referencing the substantially low polydispersity index. Forexample, the resulting polymers can have a PDI of less than 1.5, such asabout 1.05 to about 1.45.

The molecular weight of these resulting polymers can be controlled asdesired. In most embodiments, the molecular weight of the resultingpolymers can be about 2,000 g/mol to about 1,000,000 g/mole, such asabout 10,000 g/mol to about 750,000 g/mole. However, in otherembodiments, the molecular weight can be larger or smaller.

Generally, the composition of rosin-derived units (i.e., thefunctionalized resin acid(s) monomers) is primarily in the range ofabout 10% by weight to about 95% by weight (e.g., about 50% by weight toabout 80% by weight). In one particular embodiment, the resultingpolymer includes only functionalized resin acid(s) monomers (i.e., about100% functionalized resin acid(s) monomers).

However, in alternative embodiments, these resulting polymers can bearother comonomers. Particularly suitable comonomers can include thosewith polymerizable functional groups (e.g., vinyl functionality), suchas styrene, methacrylate, acrylate, lactide, caprolactone, etc, andcombinations thereof.

In one particular embodiment, the functionalized resin acid(s) monomerscan be used for preparation of block copolymers with two monomers (ABdiblock copolymer or ABA triblock copolymers) or three monomers (ABCtriblock copolymers).

In an alternative embodiment, the functionalized resin acid(s) monomerscan be used for preparation of graft copolymers, such as (i) from apolymer backbone; (ii) from a curve surface such as silicananoparticles; (iii) from a flat surface such as silicon wafersubstrates, or the like.

Additionally, the functionalized resin acid(s) monomers can be used forpreparation of star copolymers, for organic and/or inorganicnanocomposites, etc.

Rosin-derived block copolymers exhibit microphase separation, which cancombine multifunctional properties from the constituent components. Theproperties can be tuned by changing the molecular weight, compositionsand chemical structures of each segment.

In one particular embodiment, degradable polymers can be synthesizedfrom rosin based materials. Such degradable polymers can have manyapplications including packaging materials, auto parts, drug delivery,tissue engineering, membrane, gas storage, etc. Additionally, theintegration of rosin with degradable polymers can have severalbenefits: 1) more environmentally friendly, through the template ofdegradable polymers, degradation would produce residual rosin or rosinpolymers, which have much lower molecular weight (therefore morecompatible with environments) than those rosin polymers withoutdegradation templates; 2) increased renewable capacity for non-renewabledegradable polymers by increasing the volume of rosin in the degradablepolymers; and 3) new thermal, mechanical and degradability propertiesoriginating from rosin moiety.

In particular, the functionalized resin acid(s) can be co-polymerizedwith degradable comonomers. As such, the resulting copolymers caninclude the rosin-derived units in about 10% by weight to about 90% byweight, while the degradable comonomers are present in about 10% byweight to about 90% by weight. Suitable degradable comonomers caninclude caprolactone, lactide, glycolic acid, hydroxyalkanoic acids,hydroxybutyric acid, hydroxyvaleric acid, trimethylene carbonate, etc.,or combinations thereof. The comonomer can be used to form randomcopolymers, block copolymers, graft copolymers, etc.

For example, poly(2-chloro-ε-caprolactone) homopolymers can be preparedthrough ring-opening polymerization, and then converted intopoly(2-azide-ε-caprolactone) homopolymers, which click with alkynecontaining dehydroabietic moiety. Polycaprolactone is degraded underacidic conditions or bio conditions. The caprolactone unit can bereplaced by other degradable units, e.g. lactide, glycolic acid,hydroxyalkanoic acids, hydroxybutyric acid, hydroxyvaleric acid, andtrimethylene carbonate. The molecular weight of these polymers can be inthe range of about 2,000 g/mol to about 1,000,000 g/mole.

VII. Exemplary Polymerizations

In one embodiment, the synthesis of rosin-derived cationic acrylichomopolymers with controlled molecular weight is generally provided. Forexample as shown in FIG. 2, methacrylate homopolymers are prepared frommethacrylate monomers containing Diels-Alder adduct (anhydride) 3through the radical polymerization. The polymer can then be convertedinto quaternary ammonium-containing rosin-derived methacrylate polymer 4by an amidation and a quaternization reaction. The methacrylate unit canbe replaced by other monomer units, e.g. acrylates, acrylamides,styrenes. Additionally, the cationic quaternary ammonium unit can bereplaced by other cationic units (e.g. phosphonium, sulfonium, etc.).The rosin unit can be derived from other acid forms, e.g. abietic acid,through thermal isomerization.

The polymer 4 can be also prepared by post-polymerization modification,e.g. esterification reaction between poly(2-hydroxyethyl methacrylate)and compound 2. The molecular weight of these polymers is primarily inthe range of 1,000-500,000 g/mole. FIG. 2 illustrates a scheme for oneparticular embodiment—the case of quaternary ammonium-containingrosin-derived methacrylate polymer 4.

Additionally, the synthesis of rosin-derived cationic degradablehomopolymers with controlled molecular weight is generally provided. Forexample, FIG. 3 shows poly(2-chloro-ε-caprolactone) homopolymers can beprepared through ring opening polymerization.Poly(2-chloro-ε-caprolactone) homopolymers are then converted intopoly(2-azide-ε-caprolactone) homopolymers, which then click withalkyne-containing rosin-derived quaternary ammonium 5, yieldingdegradable quaternary ammonium-containing rosin-derived polycaprolactone6. Polycaprolactone is degraded under acidic conditions or compostingconditions. The caprolactone unit can be replaced by other degradableunits, e.g. lactide, glycolic acid, hydroxyalkanoic acids,hydroxybutyric acid, hydroxyvaleric acid, and trimethylene carbonate.Rosin unit can be derived from other acid forms, e.g. abietic acid,levopimaric acid, hydroabietic acid, pimaric acid. The molecular weightof these polymers is primarily in the range of 1,000-500,000 g/mole.FIG. 3 illustrates a scheme for one particular embodiment—the case ofquaternary ammonium-containing rosin-derived polycaprolactone 6.

The synthesis of rosin-containing cationic block copolymers withcontrolled molecular weight and compositions is also generally provided.For example, FIG. 4 shows a block copolymer 7 comprising of quaternaryammonium-containing rosin-derived methacrylate segment and ethyleneoxide segment that can be prepared through sequential atom transferradical polymerization. These polymers can be tuned with desirablecompositions. The molecular weight of these polymers is primarily in therange of 1,000-500,000 g/mole. The composition of rosin-derived units isprimarily in the range of 10-90 wt %. The novel method involves apolymeric composition comprising tunable rosin compositions and chemicalstructures. FIG. 4 illustrates a scheme for one particularembodiment—the case of diblock copolymers of rosin-derived methacrylateand ethylene oxide.

VIII. Resin Acid-Derived Antimicrobial Agents

Robust resin acid-derived antimicrobial agents are also generallyprovided that exhibit excellent antimicrobial activities against a broadspectrum of bacteria (6 Gram-positive and 7 Gram-negative) withselective lysis of microbial membranes over mammalian membranes. Thehydrophobicity and unique structures of resin acids can be determiningfactors in dictating the antimicrobial activity.

Bacterial contamination of food, drinking water and medical implants anddevices has posed serious threats to human health and, in some cases,has caused widespread outbreaks of infectious diseases. Development ofeffective antibacterial agents has attracted much attention as they arecapable of killing pathogenic microorganisms or preventing biofouling ofsurfaces (e.g. coating to ship hulls). Currently the majority ofsynthetic antimicrobial materials are compounds or polymers havingcationic functional groups, which promote rapid sorption onto thenegatively-charged cell surfaces of microorganisms. Many synthetic andnon-degradable polymers such as polynorbornene, polyacrylates,polyarylamides, polyesters, poly(β-lactam) and pyridinium polymers haveexhibited efficient antimicrobial activities.

In one particular embodiment, natural resin acid-derived cationiccompounds and polymers are disclosed that exhibit high antimicrobialactivities against a broad spectrum of bacteria while maintainingselective lysis on bacterial cell membranes without inducing significanthaemolysis of red blood cells over a wide range of concentrations. It isbelieved that the excellent antimicrobial activities of resinacid-derived antimicrobial compounds and polymers are a combination ofresin acids and their cationic charge.

For example, resin acids can be used as a hydrophobic component inantimicrobial agents, and be used to influence the relationship betweenantimicrobial activity and hydrophilic-hydrophobic balance. As shown inthe scheme of FIG. 8, the synthesis can be started with a highlyefficient Diels-Alder reaction between a resin acid (shown aslevopimaric acid) and maleic anhydride to produce maleopimaric acid,followed by an amidation reaction with N,N-dimethylaminoethylamine toyield compound 1. Quaternary ammonium-containing resin acid 2 can thenbe prepared by a quaternization reaction between 1 and ethyl bromide. Anesterification between compound 2 and propargyl alcohol can lead to theformation of quaternary ammonium-containing resin propargyl ester 3.

In parallel, azide-substituted poly(ε-caprolactone) (PCL) can beprepared in a multi-step route by first preparing a quaternaryammonium-containing resin acid-substituted PCL 4 via a click reactionbetween compound 3 and azide-substituted PCL in dimethylformamide withthe use of CuI/DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) as catalysts.

EXAMPLES

Examples of such rosin-containing cationic compounds and cationicpolymers are described below.

Example 1

Example 1 describes the preparation of quaternary ammonium-containingrosin acids and rosin esters, according to the exemplary method shown inFIG. 1. The synthesis for the integration of quaternary ammonium groupinto the moiety of rosin is described as follows: The abietic acid,maleic anhydride and acetic acid were mixed in a round bottom flaskunder a nitrogen atmosphere and heated at 120° C. for 12 h to yieldlevopimaric acid. The levopimaric acid is stirred withdimethylethylenediamine at 85° C. for 8 h, yielding a rosin-derivedtertiary ammonium derivative, which is then stirred with an alkyl halide(e.g. bromoethane, bromohexane, bromooctane and bromododecane) at 40° C.in tetrahydrofuran for 48 h to yield quaternary ammonium-containingrosin acid 1. The quaternary ammonium-containing rosin acid is dissolvedin thionyl chloride and refluxed for 12 h. Then, thionyl chloride isremoved by reduced pressure distillation. Ethanol, triethylamine andtetrahydrofuran are added and stirred at room temperature for 24 h toyield the ethyl ester of quaternary ammonium-containing rosin acid 2.

Example 2

This example is to prepare quaternary ammonium-containing rosin-derivedmethacrylate polymers, according to the exemplary method shown in FIG.2. The method involves the synthesis of methacrylate monomers containingDiels-Alder adduct (anhydride) by esterification, and homopolymer byfree radical polymerization. Following the amidation and quaternizationreactions, the quaternary ammonium group is introduced. A typicalprocedure for the synthesis is described as follows: levopimaric acid isdissolved in thionyl chloride and refluxed for 12 h. Thionyl chloride isremoved by reduced pressure distillation. The methacrylate monomercontaining Diels-Alder adduct (anhydride) 3 is obtained by the additionof excess 2-hydroxyethyl methacrylate (2-HEMA) and using triethylamineas catalyst. The homopolymer is prepared by the radical polymerizationof monomer 3 in the presence of the toluene and azoisobutyronitrile(AIBN). The homopolymer is dissolved in ethanol and then added with thedimethylethylenediamine. The mixture is stirred at 85° C. for 5 h andprecipitated in diethyl ether to obtain the rosin-derived tertiaryammonium homopolymer. The quaternary ammonium unit 4 is then introducedby the reaction between the rosin-derived tertiary ammonium homopolymerand alkyl halide (e.g. bromoethane, bromohexane, bromooctane andbromododecane) in tetrahydrofuran at 40° C. for 48 h.

Example 3

This example is to prepare degradable quaternary ammonium-containingrosin-derived polycaprolactone, according to the exemplary method shownin FIG. 3. The synthesis comprises of two parallel routes. First,2-chloro-ε-caprolactone and benzyl alcohol, and toluene are placed in aSchlenk flask, a solution of tin(II) 2-ethylhexanoate is added and theflask is purged with nitrogen. The mixture is stirred at 120° C. for 12h to yield poly(2-chloro-ε-caprolactone) homopolymers. Thepoly(2-chloro-ε-caprolactone) is stirred with sodium azide indimethylformamide for 24 h, yielding poly(2-azide-ε-caprolactone).Secondly, levopimaric acid is dissolved in thionyl chloride and refluxedfor 12 h and the thionyl chloride was removed by reduced pressuredistillation. Propargyl alcohol, triethylamine and tetrahydrofuran areadded and stirred at room temperature for 24 h to yield the propargylester of maleopimaric acid. Amidation reactions between propargyl esterof maleopimaric acid and dimethylethylenediamine at 85° C. for 5 h, andfollowed by a reaction with alkyl halide (e.g. bromoethane, bromohexane,bromooctane and bromododecane) at 40° C. in tetrahydrofuran for 48 hyield an alkyne-containing rosin-derived quaternary ammonium 5. At last,click reaction between poly(2-azide-ε-caprolactone) and compound 5 intetrahydrofuran at 35° C. by using CuI as the catalyst results inpolycaprolactone with a quaternary ammonium-containing rosin-derivative6.

Example 4

This example is to prepare quaternary ammonium-containing rosin-derivedblock copolymers, according to the exemplary method shown in FIG. 4.Methacrylate monomers containing Diels-Alder adduct (anhydride) 3 (seeExample 2), PEG macroinitiator, andN,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) are mixed in aSchlenk flask and purged with nitrogen. After three cycles offreeze-pump-thaw, CuBr is added into flask and stirred at 80° C. for 24h to yield block copolymer 7. The introduction of quaternary ammoniumgroup to the block copolymer is similar to the quaternization in Example2. The block copolymer and dimethylethylenediamine are dissolved inethanol and refluxed at 85° C. for 5 h, and precipitated in diethylether to obtain the rosin-derived tertiary ammonium block copolymer. Thequaternary ammonium unit is introduced by the reaction between therosin-derived tertiary ammonium block copolymer and alkyl halide (e.g.bromoethane, bromohexane, bromooctane and bromododecane) at 40° C. intetrahydrofuran for 48 h.

Example 5

This example is to prepare phosphonium salts—containing rosin acid andits ester, according to the exemplary method shown in FIG. 5). Thesynthesis is described as: The levopimaric acid, triethyl-3-[(and4-)vinylbenzyl]phosphonium chloride (I) (or II, III, IV) and acetic acidare mixed and heated (120° C.) for 12 h in a round bottom flask under anitrogen atmosphere to yield phosphonium salts-containing rosin acid 8.Synthesis of the ester of phosphonium salts—containing rosin acid 9 issimilar to the esterification reaction in Example 1.

Example 6

This example is to prepare sulfonium salts-containing rosin acid and itsester, according to the exemplary method shown in FIG. 6). The procedureof synthesis is similar to Example 5 and described as follows: A mixtureof levopimaric acid, vinyl benzyl sulfonium salt and acetic acid isstirred at 120° C. for 12 h in round bottom flask under the protectionof nitrogen to yield the sulfonium salts-containing rosin acid 10.According the method similar to Example 1, sulfonium salts-containingrosin acid is then converted into an ester 11.

Application Example Antimicrobials 1

Tests for antimicrobial activities were carried out using rosin-derivedquaternary ammonium 1 and their polymer 4 with a number-averagemolecular weight of 7.5×105 g/mol. The antimicrobial susceptibilities ofseveral Gram-negative bacteria (e.g. Pseudomonas aeruginosa, Escherichiacoli, Enterobacter aerogenes, and Klebsiella pneumonia) andGram-positive bacteria (Staphylococcus aureus and Bacillus cereus) weredetermined. These strains were purified at laboratory and maintained at−70° C. in a 1:1 mixture of glycerol and dimethylsulfoxide (DMSO). Toconduct the assays, a small volume of actively-growing cultures of eachbacterial strain is spread on agar plates, and incubated at 28° C. for24 h to form a ‘bacterial lawn’ covering the plate surface. Then 6 mm(dia) filter discs are added to the surface, and 30 ul samples(containing each compound at several concentrations dissolved in DMSO)are applied to the disc surfaces, and the plates are incubated. Thedevelopment of a clear inhibition zone around a disk is indicative ofthe compounds ability to kill bacteria (FIG. 7).

Application Example Antimicrobials 2

Referring to FIG. 8, the antimicrobial activities of the resinacid-derived compounds (2 and 3) and polymer (4) were prepared andtested against a range of pathogenic and non-pathogenic microorganisms,including Gram-negative bacteria (Pseudomonas aeruginosa, Escherichiacoli, Klebsiella pneumoniae, Proteus vulgaris, Enterobacter agglomerans,Salmonella typhimurium, Alcaligenes faecalis) and Gram-positive bacteria(Staphylococcus aureus, Bacillus cereus, Streptococcus pyogenes,Micrococcus luteus, Mycobacterium smegmatis). Initially, broth dilutionand disk-diffusion methods were compared in determining the minimalinhibitory concentrations (MICs) of 2, 3 and 4 against S. aureus, E.coli, K. pneumoniae, and P. aeruginosa as proxies for evaluating theirantimicrobial activities. The results showed that most MIC values for agiven bacterium obtained by compounds 2 and 3 and polymer 4 showedsignificantly lower MIC obtained by disk-diffusion method than the oneby broth

Considering the potential applications of antimicrobial compounds andpolymers as coatings for food packaging, medical implants and devices,and antifouling surfaces, all subsequent MIC determinations were carriedout using the disk-diffusion method. Results of the assays indicatedthat both resin acid-derived quaternary ammonium compounds (includingacid-based 2 and ester-based 3) and their polymers 4, as shown in FIG.8, exhibited strong antimicrobial activities against both Gram-positivebacteria with MICs ranging between 0.7-10.1 μM, and Gram-negativebacteria with MICs between 3-40 μM. These MIC values are comparable orbetter than many new systems developed recently. Thus, these resultsillustrated a highly efficient antimicrobial activity of these materialsagainst a broad spectrum of bacteria.

The time-dependent efficiency of antimicrobial activities of compound 3and polymer 4, of FIG. 8, against S. aureus were then investigated. Itwas observed that antimicrobial effects of the compound 3 were veryrapid, with approximately 90% of S. aureus cells being killed within 1h, while >75% strains were killed by polymer 4 in 6 h. It is believed,without wishing to be bound by theory, that the excellent antimicrobialactivities are derived from hydrophobicity of the hydrophenanthrenemoiety, which likely enhanced the penetration of the compounds/polymersinto cell membranes and subsequent killing of the bacteria. This wasfurther confirmed with control experiments, in which a quaternaryammonium compound without the resin acid moiety, tetraethylammoniumbromide (TEAB), showed no activities against both Gram-positive andGram-negative bacteria. In addition, controls consisting resinacid-derived compound 1 without quaternary ammonium also exhibitednegligible activities against all bacterial strains, and highlighted theimportance of the quaternary ammonium moiety in the observedantimicrobial activities. Results clearly showed the visual effect ofdifferent materials against S. aureus using the Agar diffusion method.

To further confirm that the antimicrobial activities were not caused byresidual copper catalysts and solvents (i.e. methanol), controlexperiments were carried out using these reagents against differentbacterial strains. However, both copper catalysts and methanol did notexhibit significant toxicity, again indicating that the antimicrobialactivities originated from resin acid-derived compounds and polymers.

BacLight LIVE/DEAD® bacterial viability assays were conducted withbacteria K. pneumoniae (Gram-negative) and S. aureus (Gram-positive)exposed to compound 3 of FIG. 8. In this assay, bacterial cells werestained using Syto-16 and propidium iodide, to distinguish live (greenfluorescence) from dead (red fluorescence) cells using confocal scanninglaser microscopy (CSLM). Results showed that the majority of S. aureusand K. pneumoniae cells were alive (i.e. green fluorescence) incontrols, but dead (i.e. red fluorescence) when exposed to compound 3.The morphology of S. aureus and E. coli cells exposed to 3 and 4 wasalso observed by field emission scanning electron microscopy (FE-SEM).FE-SEM micrographs indicated the disruption of cell membrane andsubsequent killing of bacterial cells by absorption of 3 and 4.

Haemolysis of mouse red blood cells (RBCs) was evaluated afterincubation with resin acid-derived compounds 2, 3 and polymer 4 (FIG.8). The HC50 (haemolytic concentration that resulted in 50% haemolysisof RBCs) of compound 2 was higher than 860 μM. Interestingly, compound 3displayed a HC50 of 162 μM, however, a further increase in concentrationto 810 μM did not induce the increase of haemolysis level. Polymer 4showed that the HC50 was much higher than 30 μM. The high selectivitywas manifested by the high ratios of HC50 to MIC, which were at least21-500, 6-100, and 6-44 for compound 2, compound 3 and polymer 4respectively. This indicated that our antimicrobial materials arecapable of selectively lysing microbial membranes, rather than mammaliancells.

In conclusion, novel quaternary ammonium-containing antimicrobialcompounds and polymers have been developed, which utilized natural resinacids as an active hydrophobic component. These antimicrobial materialspossessed excellent antimicrobial activity and high selectivity againstbacteria over mammalian cells. It was suggested that the highantimicrobial activity was due to the hydrophobicity and uniquestructure of natural resin acids.

As such, this work shows the potential for many other compound andpolymer systems to be applied in a similar fashion to obtain controlledproperties. The strategy described here not only offers the diversity ofstructures of different compound and polymer systems, but also tailoredproperties. It is envisioned that the successful implementation of thisstrategy will enable rosin-containing cationic compounds and polymers toreplace some petrochemical based compounds and polymers in a variety ofareas.

These and other modifications and variations to the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention, which ismore particularly set forth in the appended claims. In addition, itshould be understood the aspects of the various embodiments may beinterchanged both in whole or in part. Furthermore, those of ordinaryskill in the art will appreciate that the foregoing description is byway of example only, and is not intended to limit the invention sofurther described in the appended claims.

What is claimed:
 1. A rosin-derived cationic compound comprising acationic group attached to a conjugated diene on ahydrophenathrene-based ring of a resin acid, wherein the cationic groupcomprises a quaternary ammonium group.
 2. The rosin-derived cationiccompound as in claim 1, wherein the resin acid comprises levopimaricacid, abietic acid, dehydroabietic acid, or a mixture thereof.
 3. Therosin-derived cationic compound as in claim 1, wherein the resin acid ofthe rosin-derived cationic compound further comprises a carboxylic acidgroup.
 4. The rosin-derived cationic compound as in claim 1, wherein theresin acid of the rosin-derived cationic compound further comprises apolymerizable group attached to the resin acid via its carboxylic acidgroup.
 5. A rosin-derived polymer formed via polymerization of therosin-derived cationic compound of claim
 4. 6. The rosin-derived polymeras in claim 5, wherein the rosin derived polymer has a polydispersityindex of about 1 to about 1.5.
 7. A rosin-derived copolymer formed viapolymerization of the rosin-derived cationic compound of claim 4 and asecond monomer.
 8. The rosin-derived copolymer as in claim 7, whereinthe second monomer is a degradable monomer.
 9. The rosin-derivedcompound as in claim 4, wherein the polymerizable group comprises avinyl group.
 10. The rosin-derived compound as in claim 9, wherein thevinyl group is an acrylate group or a methacrylate group.
 11. Therosin-derived compound as in claim 4, wherein the polymerizable groupcomprises a strained ring functional group.
 12. The rosin-derivedcompound as in claim 11, wherein the strained ring functional group is acyclic ester group, a norbornene group, or a cyclopentene group.
 13. Therosin-derived compound as in claim 11, wherein the strained ringfunctional group is a caprolactone group.
 14. The rosin-derived compoundas in claim 11, wherein the strained ring functional group is a lactidegroup.